The present invention relates to a retractor (winding device) for a seat belt, and particularly to the improvement of a seat belt retractor having an emergency lock function and an automatic lock function.
Conventionally, a seat belt for keeping an occupant of a vehicle or the like on his or her seat safely is constituted by a webbing (or belt), a buckle, a mounting bracket and a retractor (winding device).
The retractor is a winding device for retracting a webbing automatically at the time of no use of the seat belt so as to prevent the webbing from being injured, and for changing the draw-out length of the webbing desirably at the time of use of the seat belt.
In an example of such a conventional retractor, at a normal time a webbing for restraining an occupant is allowed to be drawn out and wound desirably, so as to avoid such a problem that excessive restraining of the occupant gives an oppressive feeling to the occupant. On the other hand, an inertia detecting device responding to sudden acceleration or deceleration of the vehicle is provided to add an emergency lock function for locking a winding shaft of the webbing so that the webbing is prevented from being drawn out by use of the reaction of the inertia detecting device at the time of sudden acceleration or deceleration of the vehicle to thereby ensure the safety of the occupant. Hereinafter, the term "ELR" means an emergency locking retractor.
However, in the case of such an emergency lock function, it is impossible to prevent the webbing from being drawn out at a normal time. Accordingly, when a baggage, an auxiliary child seat (child seat), or the like, is set on a seat by use of the webbing, the webbing is gradually drawn out of the retractor by vibration or the like during the running of the vehicle, so that there is a fear that the attachment of the child seat or the like becomes loose.
Therefore, as disclosed in U.S. Pat. No. 4,811,912, Unexamined Japanese Utility Model Publication No. Hei. 3-126745, Unexamined Japanese Utility Model Publication No. Hei. 5-72612, and so on, independently of such an emergency lock function, an automatic lock function is provided for preventing a webbing from being drawn out after the setting of the webbing regardless of normal time or a case where sudden acceleration or deceleration of the vehicle occurs. Hereinafter, the term "ALR" means an automatic locking retractor. Then the automatic lock function is operated when a baggage, a child seat, or the like, is set on a seat, and the emergency lock function is operated when an occupant is restrained.
A seat belt retractor disclosed in those publications has the above-mentioned emergency lock function, and is designed so that the automatic lock function can be switched between its active state and its inactive state by proper operation of the state where the retractor winds a webbing.
A seat belt retractor disclosed in Unexamined Japanese Utility Model Publication No. Hei. 5-72612 provides a rotation lock device for engaging with a winding shaft of the retractor winding a webbing so as to lock the rotation of the winding shaft in the webbing draw-out direction; and a lock device driving mechanism for controlling the operation of the rotation lock device to form a lock state where the rotation lock device is engaged with the winding shaft to thereby prevent the winding shaft from rotating in the webbing draw-out direction, or a non-lock state where the rotation lock device is kept not so as to engage with the winding shaft so that the winding shaft is allowed to rotate in the webbing draw-out direction. The seat belt retractor further provides an operation mode switching device for setting and switching the operation mode of the lock device driving mechanism so as to be switchable between an ELR mode (emergency lock mode) where the lock device driving mechanism is operated as an emergency lock mechanism to bring the rotation lock device into the lock state in an emergency of sudden acceleration or deceleration of the vehicle or the like, and an ALR mode (automatic lock mode) where the lock device driving mechanism is operated as an automatic lock mechanism to bring the rotation lock device into the lock state whether in an emergency or not.
The operation mode switching device has an operation mode switching lever attached pivotably between an ELR mode position for setting the ELR mode and an ALR mode position for setting the ALR mode; a control plate which rotates in interlocking with the winding shaft to thereby reflect the state of the webbing wound on the winding shaft; and a guide groove provided on the control plate and guiding a guide pin provided and projecting on the operation mode switching lever, so as to control the swing of the operation mode switching lever in accordance with the state of the webbing wound on the winding shaft.
In the conventional seat belt retractor, which has such a configuration, the automatic lock function can be actuated selectively by the operation of the state of the wound webbing.
Further, in the above-mentioned Publication, the guide groove has an outer cam groove for receiving the guide pin of the operation mode switching lever, and holding the operation mode switching lever in the ELR mode position in a period from the time when the quantity of the webbing wound is the maximum to the time when a constant amount of the webbing is drawn out; a narrow groove portion (cam groove) formed to be connected to the end point of the outer cam groove, and for receiving the guide pin and holding the operation mode switching lever in the ELR mode position until the webbing is further drawn out up to the minimum winding quantity after the constant amount of the webbing is drawn out; and a wide groove portion (inner cam groove) formed so as to connect the start point of the narrow groove portion onto the way of the outer cam groove, and for receiving the guide pin returned, by the winding of the webbing, to the start point of the narrow groove portion, and holding the operation mode switching lever in the ALR mode position until the webbing is further wound up to a predetermined quantity. Further, in order to prevent the operation mode switching lever from being moved to an opposite mode position unexpectedly by the vibration of a vehicle or the like, there is provide such a technique that an urging force is given to the operation mode switching lever by a snap action spring or the like by which the urging direction is changed by use of the central, neutral position between the ELR mode position and the ALR mode position as a border.
A seat belt retractor disclosed in U.S. Pat. No. 4,811,912, Unexamined Japanese Utility Model Publication No. Hei. 3-126745 has a well-known emergency lock mechanism having a rotation lock device for engaging with a winding shaft to thereby lock the rotation of the winding shaft in the webbing draw-out direction, and an inertia detecting device for actuating the rotation lock device in an emergency of a vehicle; and an operation mode switching device for operating the inertia detecting device in accordance with the state of the wound webbing to thereby suitably move the rotation lock device to an engagement position or a disengagement position with the winding shaft. If the operation mode switching device makes the rotation lock device engage with the winding shaft, the rotation of the winding shaft in the webbing draw-out direction is locked so as to actuate an automatic lock mechanism.
Further, as an operation mode switching device used in such a seat belt retractor, for example, an operation mode switching lever (operating lever) which is movable between a position where the inertia detecting device is operated and a position where it is not operated, and a control plate (operating member) displaced relatively to the operation mode switching lever in accordance with the rotation of the winding shaft, are provided for bringing the rotation lock device to the engagement position or the disengagement position with the winding shaft. Since the operation mode switching lever is moved by the control plate, the operation mode switching lever swings between a position where the inertia detecting device is operated and a position where it is not operated, in accordance with the state in which the webbing is wound on the winding shaft. As a result, the rotation lock device is taken to the engagement position or the disengagement position.
Such an operation mode switching lever as disclosed in U.S. Pat. No. 4,811,912, Unexamined Japanese Utility Model Publication No. Hei. 3-126745 is urged to the position where the inertia detecting device is operated or the position where not operated, by an urging device (for example, a so-called snap action spring) designed to change the urging direction in the border of a neutral position by use of an over center spring, a compression spring, or the like, in accordance with necessity.
When the automatic lock mechanism is in operation, the operation mode switching lever keeps the inertia detecting device in operation by the urging force of the urging device in order to dispose the rotation lock device in the engagement position. However, if the urging device is moved beyond the neutral position by the effect of vibration, shock, or the like, which acts on the operation mode switching lever during the running of a vehicle, the urging direction of the urging device is changed over, so that the operation mode switching lever is urged in the direction in which the inertia detecting device can not be kept in operation. Then the operation mode switching lever cannot dispose the rotation lock device in the engagement position. Accordingly there is a possibility that the retractor is released from the automatic lock state.
Therefore, when a baggage, a child seat or the like is set on a seat by use of the webbing, there is a fear that the seat belt retractor is released from the automatic lock state by vibration, shock or the like during the running of a vehicle so as to return to its emergency lock state, and the webbing is therefore drawn out of the retractor gradually during the running of the vehicle to thereby loosen the attachment of the baggage, the child seat or the like.
In the case of a seat belt retractor disclosed in Unexamined Japanese Utility Model Publication No. Hei. 5-72612, in order to solve the foregoing problem, a guide groove for controlling the swing of an operation mode switching lever has a cam groove for guiding a guide pin of the operation mode switching lever. A cam surface, which is a side surface of the cam groove, contacts with the guide pin so that the operation mode switching lever is prevented from swinging to an improper mode position.
However, in the case of this seat belt retractor disclosed in Unexamined Japanese Utility Model Publication No. Hei. 5-72612, a narrow groove portion guides the guide pin until a predetermined length of the webbing is completely wound after the webbing is drawn out up to the maximum. In the position where this narrow groove portion guides the guide pin, the operation mode switching lever moves slightly toward the ALR mode position beyond the neutral position, so that the urging device changes its urging direction toward the ALR mode position. However, near the neutral position, the urging force of the urging device is so weak, and the section where the narrow groove portion guides the guide pin is comparatively so long, that the movement toward the ALR mode position is continuously prevented on the way during the guide of the narrow groove portion. Even if the guide pin reaches a wide groove portion, the operation of moving to the ALR mode position is delayed or so, so that there is a fear that the operation of the automatic lock function goes wrong.